1. Field of the Invention
The present invention relates to a cutting insert installed in an indexable cutting tool.
2. Description of the Related Art
A cutting insert has been known which is shaped like a polygonal plate and which includes a cutting edge formed at an intersecting portion between an upper surface and each side surface of the cutting insert. To allow chips to be appropriately processed, the cutting insert includes a chip breaker groove formed between a central portion thereof and each corner cutting edge formed at a corresponding one of the corner portions of the upper surface, with a chip breaker projection provided in the chip breaker groove.
A cutting insert described in Japanese Patent Laid-Open No. H06-190612 (1994) is characterized by (a) including projecting portions each projecting from the central portion thereof into the chip breaker groove toward the corresponding corner cutting edge and protruding portions each projecting beyond the corresponding projecting portion toward the corresponding corner cutting edge and (b) in that an inclined raised portion is provided between the protruding portion and the chip breaker groove.
However, in the cutting insert described in Japanese Patent Laid-Open No. H06-190612 (1994), the raised portion of the protruding portion is a flat inclined surface, resulting in a large contact area between the raised portion and chips. This tends to increase cutting resistance (frictional resistance) between the chips and the cutting insert. Moreover, the cutting insert has a two-stage construction including the projecting portion projecting toward the corner cutting edge and the protruding portion projecting beyond the projecting portion toward the corner cutting edge. Thus, if an attempt is made, at a large depth of cut, to allow the chips to contact the projecting portion and thus to be curled, the protruding portion may excessively block the chips to increase the cutting resistance, depending on cutting conditions.
If the cutting insert in Japanese Patent Laid-Open No. H06-190612 (1994) is redesigned so as to operate effectively at a large depth of cut in order to cope with the above-described problem, then at a small depth of cut, the chips are insufficiently blocked and thus unstably curled.